1. Field of the Invention
The present invention relates to an image-bearing member protecting agent, a protective layer forming device, an image forming method, an image forming apparatus and a process cartridge, and more specifically relates to an image forming apparatus, such as a copier, facsimile, printer, plotter, and complex machine provided with these multiple functions, an image-bearing member protecting agent for protecting a surface of an image bearing member of the image forming apparatus, a protective layer forming device for forming a protective layer on the surface of the image bearing member using the image-bearing member protecting agent, an image forming method using the image-bearing member protecting agent and a process cartridge used in the image forming apparatus.
2. Description of the Related Art
Conventionally, in electrophotographic image formation, a latent electrostatic image is formed on an image bearing member made from a photoconductive material, etc. and charged toner particles are attached to this latent electrostatic image so as to form a visible image. The visible image formed using the toner particles is transferred onto a transfer medium such as paper, or the like, and then fixed on the transfer medium utilizing heat, pressure, solvent gas, or the like so as to form an output image.
Methods for the image formation are broadly classified, according to methods for charging toner particles to form a visible image, into so-called two-component developing methods in which frictional charging effected by stirring and mixing toner particles and carrier particles is utilized, and so-called one-component developing methods in which toner particles are charged without using carrier particles. Further, the one-component developing methods are classified into magnetic one-component developing methods and nonmagnetic one-component developing methods, according to whether or not magnetic force is utilized to keep toner particles on a developing roller.
In image forming apparatuses, such as copiers, complex machines based upon the copiers, and the like for which high-speed processing capability and image reproducibility are required, the two-component developing methods have been employed in many cases due to demands for stable chargeability of toner particles, stable charge rising properties of the toner particles, long-term stability of image quality, and the like; whereas in compact printers, facsimiles, etc. for which space saving, cost reduction and the like are required, the one-component developing methods have been employed in many cases.
Also, nowadays in particular, colorization of output images is progressing, and demands for improvement of image quality and stabilization of image quality are increasing like never before.
For the improvement of image quality, toners have been made smaller in average particle diameter, and particles of the toners have been made rounder in shape with their angular parts removed.
Generally, in an image forming apparatus which operates in accordance with any such electrophotographic image forming method, regardless of which developing method is employed, a drum-shaped or belt-shaped image bearing member (typified by a photoconductor) is uniformly charged while being rotated, a latent image pattern is formed on the image bearing member by laser light or the like, and the latent image pattern is visualized as a toner image by a developing unit and transferred onto a transfer medium.
After the toner image has been transferred onto the transfer medium, untransferred toner components remain on the image bearing member. If such residues are directly conveyed to a region for the charging step, it often hinders the image bearing member from being uniformly charged; accordingly, in general, the toner components, etc. remaining on the image bearing member are removed by a cleaning unit in a cleaning step after the transfer step, thereby bringing the surface of the image bearing member into a clean enough state, and then charging is carried out.
Thus, the image bearing member surface is exposed to various types of physical stress and electrical stress in steps of image formation, i.e. each step of charging, developing, transferring and cleaning, and the like, and the image bearing member, charging member, and cleaning member are deteriorated with time. In attempts to solve this problem, a number of proposals for lubricants and methods of supplying lubricant components and forming films have been made thus far to reduce deterioration of the image bearing member, charging member, and cleaning member.
For example, Japanese Patent Application Publication (JP-B) No. 51-22380 proposes a method of forming a lubricant film on a photoconductor surface by supplying the photoconductor surface with a solid lubricant composed mainly of zinc stearate in order to lengthen the lifetimes of a photoconductor and a cleaning blade.
Japanese Patent Application Laid-Open (JP-A) No. 2001-305907 discloses an example of use of a lubricant coating device as a specific method of coating a solid lubricant. The lubricant supply device includes a brush roller (a brush-shaped member, supply member) configured to come into contact with the solid lubricant molded into a bar shape, and to rub the solid lubricant so as to scrape off the solid lubricant and then supply the powdered lubricant to a photoconductor belt or an intermediate transfer belt (a lubricant supplying target). The solid lubricant is held with a solid lubricant holding member, and a spring (a biasing unit) is in contact with the solid lubricant holding member. The solid lubricant is pressed against the brush roller by the biasing force of the spring. When the brush roller is rotated, the solid lubricant being in contact with the brush roller is rubbed by the brush roller and scraped off and adhered to the brush roller, and then the lubricant adhered to the brush roller is applied and adhered to the surface of the photoconductor belt or the intermediate transfer belt. Further, a lubricant leveling blade is provided in the lubricant supply device. The lubricant leveling blade presses and spreads the lubricant on the surface of the photoconductor belt or the intermediate transfer belt, so that a lubricant layer having a uniform thickness is formed on the surface of the photoconductor belt or the intermediate transfer belt.
However, in the technique disclosed in JP-A No. 2001-305907, it has a structure such that a spring is in contact with the solid lubricant so as to press the solid lubricant against the brush roller, and the spring is extended as the solid lubricant is scraped off. Thus, the pressing force is inevitably weakened. As a result, the amount of the solid lubricant scraped decreases, and accordingly the amount of the solid lubricant supplied to the photoconductor and intermediate transfer belts decreases. Therefore, the photoconductor and intermediate transfer belts cannot be sufficiently protected over time.
To solve these problems, JP-A No. 2007-293240 proposes that a plurality of moving members are provided to a member holding a solid lubricant so as to press the moving members against the member holding the solid lubricant, and a pressure is applied to the moving members by a spring member so that a certain pressure can be maintained with respect to the brush roller, even though the solid lubricant is scraped off with time.
Moreover, to solve the problem that the photoconductor and intermediate transfer belts cannot be sufficiently protected over time due to the decrease in the amount of the solid lubricant, JP-A No. 2007-65100 proposes that the hardness of the solid lubricant is altered in the direction from the front surface to the rear surface of the solid lubricant, specifically, the hardness of the front surface, which is a side of the solid lubricant to be used at the beginning, is made higher than that of the rear surface, which is a side thereof to be left when most of the image-bearing member protecting agent is used up, so that the decrease in the amount of the consumption can be prevented.
However, it has been known that the technique disclosed in JP-A No. 2007-293240 cannot prevent the solid lubricant block (lump) obtained by compression molding from decrease in consumption with time even though the applied pressure is maintained over time. This will be exemplified in Comparative Example below.
In the technique of JP-A No. 2007-65100, there is no suggestion of a specific means for attaining a solid lubricant block having different hardness between the front surface and the rear surface. That is, JP-A No. 2007-65100 discloses that a plurality of solid lubricant blocks each having different hardness are stacked, and used. However, there is no description of the means for attaining the solid lubricant blocks formed of the same materials and each having different hardness. If the hardness is varied by changing the compositions of the solid lubricant, the same quality cannot be maintained over time.
Moreover, if the solid lubricant blocks formed of the same materials and each having different hardness are stacked and used, the inflection point of the consumption of the solid lubricant is caused due to the boundaries of the blocks. In this case, the same quality cannot be also maintained over time.
On the other hand, it has been known that the fatty acid metal salts such as zinc stearate disclosed in JP-B No. 51-22380, JP-A Nos. 2001-305907, 2007-293240, and 2007-65100 may lose lubricity in early stages due to the influence of discharge performed near the image bearing member in a charging step (For example, see the paragraph [0007] in JP-A No. 2008-310162). As a result, the lubricity of the cleaning blade and the image bearing member is lost, and toner passes through the cleaning blade, forming defect images.